Staple orienting apparatus

ABSTRACT

Apparatus for casting uncured solid propellant having metal staples disbursed therein, which apparatus is a container having a discharge opening covered by a fine mesh screen or a plate with multiple openings. A means is operably associated with the container for forcing the staple containing propellant through the screen whereby the staples within the propellant are oriented in the direction of propellant flow and the propellant is deposited in the casting with the staples in a planar orientation.

United States Patent (1 1 Lista et al.

l STAPLE ORIENTING APPARATUS {75] inventors: Edwin L. Lista, Roseville; Kenneth S. Williams, Sacramento, both of Calif.

[73] Assignee: Aerojet-General Corporation, El

Monte, Calif.

[22] Filed: Oct. 6, 1969 2: Appl. No.: 866,088

Related U.S. Application Data [63] Continuation of Ser. No 52l,757, Jan. [8, I966.

[52] U.S. Cl 86/1; lOZ/lOl; 264/3 R [Sl] Int. Cl .r C06b 21/00 [58] Field of Search 86/20, l; lOZ/lOl, 99;

[56] References Cited UNITED STATES PATENTS 3311.678 3/1967 Brock et al. v. 86/20 X June 24, 1975 3359350 l2/l967 Godfrey ..86/lX Primary Examiner-Benjamin A. Borchelt Assistant Examiner-H. J. Tudor Attorney, Agent, or Firm-Edward O. Ansell [57] ABSTRACT Apparatus for casting uncured solid propellant having metal staples disbursed therein, which apparatus is a container having a discharge opening covered by a fine mesh screen or a plate with multiple openings. A means is operably associated with the container for forcing the staple containing propellant through the screen whereby the staples within the propellant are oriented in the direction of propellant flow and the propellant is deposited in the casting with the staples in a planar orientation.

5 Claims, 5 Drawing Figures PATENTED JUN 2 4 I975 SHEET m M H N E m M W a 59 T T Lm A WE r w m5 STAPLE ORIENTING APPARATUS This is a continuing application of our copending application Ser. No. 521,757 filed Jan. l8, 1966, entitled Staple Orienting Method and Apparatus."

This invention relates to a novel apparatus for increasing the performance of solid rocket propellant which includes the orientation of metallic staples disbursed throughout the propellant.

It is well known that the addition of metal staples, such as wires, filaments, strips, and the like, will increase the burning rate of solid propellant rocket motors. These staples which have a substantially higher thermal difusivity or conductivity and the solid propellant material serve as miniature heat conductors. The increased burning rate results from the fact that the metal staples effect rapid heat transfer from the high temperature combustion gases in the flame zone to the unburned propellant in the grain. In this manner the flame propagates rapidly along the metal staples. As a result, the burning surface travels along the metal sta ple (heat conductor) at a much faster rate than the normal propellant burning rate. In addition, the burning surface recesses to form a cone with the metal staple at its apex and thereby becoming much larger than normal. This greatly increases the effective burning rate of the propellant grain along with the rate of gas evolution.

In a solid rocket motor the maximum increase in burning rate obtained from the metal staples can only be achieved if the staples are oriented perpendicular (normal) to the burning surface of the propellant. Methods of dispersing metal staples within the solid propellant matrix, however, inevitably resulted in a random orientation of the staples. While the random orientation achieved measurable increases in burning rates, it did not produce optimum results and oftentimes results in uneven burning. This is true for both end burning and internal burning grains.

It is therefore an object of this invention to provide an improved method for increasing the performance of solid propellant rocket motors.

Another object of this invention is to provide an improved method of orienting metallic staples disbursed within a solid propellant rocket motor.

A further object of this invention is to provide an improved bayonet for casting solid propellant having metal staples disbursed therein.

These and other objects of this invention will be apparent from the detailed description which follows when taken together with the appended drawings wherein:

FIG. 1 is a cross-sectional view of an end-burning solid propellant rocket motor casing and bayonet of the present invention during the casting process;

FIG. 2 is a cross-sectional view of an internal burning solid propellant rocket motor, casing and bayonet of the present invention during the casting process;

FIG. 3 is a cross-sectional view of the casing of FIG. 2 taken along line 3-3 of FIG. 2;

FIG. 4 is a cross-sectional view of a casting bayonet similar to that shown in FIG. 1 except that it is modified to show a second screen and to show a pressurizing means similar to that utilized for the casting bayonet shown in FIG. I; and

FIG. 5 is a cross-sectional view of the bayonet of FIG. 4 taken along the line 5-5 of FIG. 4.

The metallic staples which are employed as burning rate additives in solid propellants are comprised of any metal or metal alloy of high heat conductivity and high melting point, such as copper, aluminum, iron, stainless steel, hafnium, brass, zirconium, silver, and many others. These staples, which may be of any cross-section, such as circular, rectangular, square, or many-sided, can vary in length up to and in some cases exceeding 500 mils. In the usual case, however, all of the staples in a given matrix will be of the same length and have a maximum side-to-side dimension of approximately 20 mils.

The solid rocket propellant composition is mixed in the normal manner and the staples added at some point in the process prior to the casting of the propellant. The dispersion of the staples in the propellant during the mixture thereofwill result in a random or uneven orien tation of the staples in the mixture. An example of a staple-containing propellant is taught in copending application Ser. No. 338,527 by Ralph W. Lawrence, filed Jan. 17, I964, now US. Pat. No. 3,793,097 and assigned to the same Assignee as the present invention.

Referring now to FIG. 1 there is shown a propellant casting tube or bayonet 10 inserted within an endburning rocket motor casing 12. Bayonet 10 comprises a long, cylindrical tube 14, having a wire cloth or screen 16 at the bottom thereof. The top of the tube I4 is fitted with a flange 18. A cover plate 20 over the top of the tube I4 effects a pressure seal with the tube flange I8 when used with an O-ring 22. A tri-clover fitting can also be used to effect this pressure seal. A fitting 24 (such as a Hanson fitting) threaded into the cover plate 20 provides access for a pressurized fluid to the top of the tube I4. A connecting line 32 joins the fitting 24 with a source 30 of gas, such as nitrogen under pressure.

The tube 14 ofa structural material, such as stainless steel, is filled under vacuum with a solid propellant 26 having disbursed within it randomly oriented metal staples 28. The screen 16 retains the propellant within the tube when there is no external pressure applied to the propellant 26. The size of the openings in the screen 16 will depend primarily upon the dimensions of the staples and would normally be between 2% and 4 mesh. Additionally, more than one screen may be utilized at the bottom of the tube 14 e.g., a Zia-mesh screen over a 4-mesh screen.

The bayonet 10, once it has been filled with propellant, is inserted screen-end down into the motor casing 12 so that the screen 16 of the bayonet is only a short distance from the bottom of the casing 12. The outside diameter of the bayonet tube 14 should be only slightly smaller than the inside diameter of the casing 12. By applying pressure to the top of the propellant 26 by such means as a compressed or pressurized gas admitted through the fitting 24 the propellant is forced through the screen 16 at the bottom of the tube I4 and into the rocket motor casing 12. Alternately, a mechanical or hydraulic displacement technique can be used to force the propellant through the screen 16.

The screen 16 through which the propellant containing the randomly oriented metal staples 28 is forced, orients the metal staples in a direction perpendicular to the plane of the screen. The openings of the screen I6 are too small to permit the metal staples to proceed through in any other orientation.

As the propellent 26 with the metal staples 28 now oriented along axis of the motor casing fills the motor casing 12 the bayonet is raised to permit the propel lant to substantially fill the casing 12. The screen 16 of the bayonet 10 may be kept a short distance from the propellant already deposited or cast into the motor or may be in contact with the deposited propellant such that the propellant offers a slight resistance to the flow which helps to align the staples. The propellant will, in effect, flow from the bayonet into the casing as a viscous fluid under pressure. In this manner the propellant cast into the motor casing retains the staple orientation resultant from passing through the screen. This cast propellant can now be cured in the conventional manner as if there were no staples disbursed therein.

With the metal staples oriented along the axis of the motor casing, the staples will be normal to the burning surface of an end-burning propellant grain. Thus, there will be provided the maximum increase available in the burning rate from the use of the added metal staples.

Should for any reason it be desirable to provide the staples thus oriented in an internal burning motor a central void could be provided in the bayonet 10 to enable the bayonet to be inserted into the casing 12 within a core in place. Such a staple orientation would normally, however, be undesirable for an internal burning motor.

Referring now to FIG. 2, there is shown a bayonet 40 positioned over an internal burning solid propellant rocket motor casing 42. A core 44 is positioned in the central portion of the casing 42.

The bayonet 40 comprises a tube 46 which is shown as a truncated conical section with the base of the conical section upward. A fine mesh cloth, perforated plate, or wire screen 48 extends across the lower end of the tube 46 which is positioned over the upper end of the casing 42. A diaphragm 50 is positioned in the screen 48 directly over the core 44 of the casing 42. The diaphragm 50 may be connected to a vibrator 54 external to the bayonet 40 by means of a hollow rod 52. The bayonet 40 would be filled with a solid propellant 56 in which metal staples 58 are randomly dispersed.

FIG. 4 is an alternate arrangement of the bayonet 40 shown in FIG. 2. In FIG. 4 the bayonet 41 is comprised of a tube 46 which is a truncated conical section with the base of the conical section upward. A fine mesh cloth or perforated plate or wire screen 48 extends across the lower end of the tube 46 and has a second fine mesh cloth, perforated plate, or wire screen 49 extending across the lower portion of the tube 46 immediately above the first screen 48. The second or upper screen 49 may be a 2Vz-mesh screen over the lower screen 48, which may be a 4-mesh screen. A diaphragm 50 is positioned in the screen 48 in the approximate center thereof. The top of the tube 46 is fitted with a flange 18. A cover plate over the top of the tube 46 effects a pressure seal with a tube flange 18 when used with an O-ring 22. A fitting 24 threaded into the cover plate 20 provides access for a pressurized fluid to the top ofthe tube 46. A connecting line 32 joins the fitting 24 with a source of gas such as nitrogen under pressure. The diaphragm 50 may be connected to a vibrator 54 external of the bayonet 41 by means of a hollow rod 52 extending through the cap 20 which is provided with a pressure seal by the use of an O-ring 23. The bayonet 41 would be filled with a solid propellant having metal staples randomly dispersed therein.

With the bayonet 40 as shown in FIG. 2 positioned over the casing 42 the propellant 56 containing the staples 58 will, either due to gravity or as a result of an externally applied pressure, pass through the screen 48. The openings of the screen 48 are such as to produce a large number of elongated propellant droplets 60, with each droplet having the metal staples oriented along its axis of elongation. A means for encouraging the formation of droplets rather than string-like extrusions would be employed, which means may include controlling the rate of casting so that the propellant will break off in the form of droplets or employing a rotatable or pivotal screen, not shown, which screen may be suspended immediately below the screen 48. In the alternate embodiment shown in FIGS. 4 and 5 the propellant is forced through the screen 49 to initiate staple orientation prior to being forced through the screen 48. In either embodiment of FIG. 2 or FIG. 4 the openings in the screen 48 are sufficiently small that as propellant is forced therethrough the weight of the propellant will be sufficient to cause the propellant to break and form droplets as shown in FIG. 2. The droplets 60 will then fall to the bottom of the casing 42. The staples within the propellant which is in the bottom of the casing 42 will have planar orientation, as shown in FIG. 2, however, within the plane the staples 58 may have ran dom orientation, as shown in FIG. 3.

It has been experimentally demonstrated that although the droplets 60 tumble in random directions as they fall to the bottom of the casing 42 they will come to rest in the bottom of the casing with their axis of elongation in a plane perpendicular to the axis of the casing 42. Thus, regardless of the angle at which the droplets hit the partially filled propellant in the bottom of the casing, they flop over on their side before coming to rest. In this manner, the staples are oriented in a plane normal to the axis of the casing. The diaphragm 50 prevents droplets 60 from falling directly upon the core 44.

This planar randomization of the staples permits even burning of the propellant. Conventional casting of the propellant around the core 44 has been known to partially orient the staples which resulted in uneven burning characteristics for the propellant. The planar randomization will not, however, produce the maximum burning rate achievable with the metal staples, which requires that the staples be oriented normal to the burning surface. In the case of an internal burning motor, this requires a radial orientation of the staples.

To achieve this radial orientation, the screen 48 can be vibrated up and down by means of a vibrator with the greatest amplitude at the center of the screen 48 at the point where the rod 52 is attached to the diaphragm 50 of screen 48. The vibration will give the individual droplets of propellant falling from the screen 48 as a radial moment, either toward or away from the center of the screen 48. This radial momentum will result in the droplets 60 achieving a radial orientation in the casing 42 and thereby orient the staples normal to the propellant burning surface, which will produce a maxim um burning rate from the staples.

While preferred forms and embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that modification can be made without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.

What is claimed is:

I. An apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein comprising:

a tube for containing the uncured solid propellant;

and

a fine mesh screen fixedly attached to the bottom end of said tube, said screen having openings therein whereby when the solid propellant passes through said screen, the metal staples of said propellant are oriented in the direction of propellant flow.

2. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition:

a means for applying pressure to the top of the propellant in said tube to force said propellant through said screen.

3. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition:

a means for vibrating said screen to impart a radial moment to the propellant leaving said screen 4. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim I, and in addition:

a second fine mesh screen fixedly attached to said tube adjacent the bottom thereof and above the other screen, said second screen having openings therein whereby said second screen initiates staple orientation in the direction of propellant flow.

5. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition:

means operably associated with said screen for encouraging said propellant to form into droplets. 

1. An apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein comprising: a tube for containing the uncured solid propellant; and a fine mesh screen fixedly attached to the bottom end of said tube, said screen having openings therein whereby when the solid propellant passes through said screen, the metal staples of said propellant are oriented in the direction of propellant flow.
 2. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition: a means for applying pressure to the top of the propellant in said tube to force said propellant through said screen.
 3. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition: a means for vibrating said screen to impart a radial moment to the propellant leavinG said screen.
 4. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition: a second fine mesh screen fixedly attached to said tube adjacent the bottom thereof and above the other screen, said second screen having openings therein whereby said second screen initiates staple orientation in the direction of propellant flow.
 5. The apparatus for casting uncured solid propellant having elongated metal staples randomly dispersed therein as described in claim 1, and in addition: means operably associated with said screen for encouraging said propellant to form into droplets. 